Hand-held calculators are widely used in the building trade, for example in estimating the cost of materials such as pipes, condits, ducts, wiring and cabling. They are likewise useful in calculating such things as the cost of real estate and the heating and air conditioning requirements of a building.
However, the usefulness of calculators in such operations is somewhat restricted. For example in estimating the cost and material required for a heating, plumbing or wiring installation in a building, the architect or engineer must first obtain certain measurements, for example by measuring a scale drawing with a ruler and feed these measurements into the calculator. He must thus perform the two successive functions of first obtaining the measurement values and then using these values in his calculations.